1. Field of the Invention
This invention relates to an optical information recording-reproducing apparatus for optically recording or reproducing information on an information recording medium, and more particularly to an optical information recording-reproducing apparatus having the function of applying a plurality of reproducing spots at a time.
2. Related Background Art
The following forms of a recording medium for optically recording information thereon or reading out recorded information therefrom, are known: a disc-like form a card-like form; and a tape-like form. These optical information recording media include one capable of recording and reproducing and one capable of reproducing only. Particularly, the card-like recording medium (hereinafter referred to as the optical card) is expected to have its use expanded because of its ease of manufacture, good portability, and the good accessibility thereof.
Various optical information recording-reproducing apparatus directed to such an optical card have been proposed, and in any one of them, the recording and reproduction of information are effected while auto-tracking and auto-focus control are always effected. Also, as regards the recording of information onto the recording medium, a light beam modulated in accordance with recording information and stopped down into a micro light spot is scanned on an information track, whereby information is recorded as an optically detectable information bit string. The reproduction of information from the recording medium is effected by scanning a light beam spot of such a degree of constant power that recording is not effected on the recording medium on the information bit string of the information track, and detecting the reflected light from or the transmitted light through the recording medium at this time. As such an information recording-reproducing apparatus, there is also known an apparatus for reproducing data from a plurality of tracks at a time.
FIG. 1 of the accompanying drawings shows an example of an optical system (optical head) used in an optical information recording-reproducing apparatus for reproducing information of a plurality of tracks at a time. In FIG. 1, reference numeral 101 designates a semiconductor laser provided as a light source for recording and reproduction. A light beam emitted from the semiconductor laser 101 is collimated by a collimator lens 102, whereafter it is divided into a plurality of light beams by a diffraction grating 103, and is condensed on an optical card 107 via a polarizing beam splitter 104, a quarter wavelength plate 105 and an objective lens 106. The reflected light from the optical card 107 enters a photodetector 109 via the objective lens 106, the quarter wavelength plate 105, the polarizing beam splitter 104 and a toric lens 108. At this time, recording, reproduction and auto-focus control (hereinafter referred to as AF) are effected by the use of 0-order diffracted light of the light beams divided by the diffraction grating 103, auto-tracking control (hereinafter referred to as AT) is effected by the use of .+-. first-order diffracted light, and the reproduction of data from an adjacent track is effected by the use of .+-. second-order diffracted light. AF is of the astigmatic type, and AT is of the three-beam type.
FIG. 2A of the accompanying drawings is a schematic plan view showing the optical card 107 used in the information recording-reproducing apparatus as described above. A number of information tracks for recording and reproducing information are arranged in parallel on the optical card 107, and some of them are designated as T1, T2 and T3. These information tracks are demarcated by tracking tracks tt1-tt4. The tracking tracks tt1-tt4 are formed by grooves or a substance differing in reflectance from the tracks T1-T3, and are used as guides for obtaining a tracking error signal.
Also, reference numeral 112 designates the light spot of 0-order diffracted light, reference numerals 111 and 113 denote the light spots of .+-. first-order diffracted light, and reference numerals 110 and 114 designate the light spots of .+-. second-order diffracted lights. These five light spots are disposed on straight lines having a predetermined angle of inclination .theta. with respect to the tracks, and the light spot 112 lies on the central track T2, the light spots 111 and 113 lie on the tracking tracks tt2 and tt3, respectively, and the light spots 110 and 114 lie on the tracks T1 and T3, respectively, adjacent to the track T2. That is, these light spots are disposed rotation-symmetrically with respect to the central light spot 112. The light spot 112 is used for recording, reproduction and focus control as previously described, the light spots 111 and 113 are used for tracking control, and the light spots 110 and 114 are used for reproduction. Accordingly, in the case of reproduction, three tracks can be reproduced at a time by the light spots 110, 112 and 114.
These light spots scan over the optical card 107 from left to right as viewed in FIG. 2A by a mechanism, not shown, while keeping the same positional relation, whereby the recording or reproduction of information is effected. This scanning system may be of a type in which the optical system is moved or a type in which the optical card is moved, but in any of these types, the optical system and the optical card are reciprocally moved relative to each other and therefore, portions which are not at a constant velocity are created at the opposite ends of the optical card. This state is shown in FIG. 2B of the accompanying drawings. The abscissas axis of FIG. 2B represents the left to right direction of the optical card, and the ordinate axis represents the scanning velocity. When the light spots are to be scanned from left to right in FIG. 2B, acceleration is first effected in an acceleration region, and when a predetermined velocity is reached, scanning is effected at a constant velocity, and when a predetermined position is reached, deceleration is effected during a deceleration period, and the scanning of a track is terminated.
Further, as shown in FIG. 2A, track numbers Tn1L, Tn2L, Tn3L and Tn1R, Tn2R, Tn3R for identifying the respective tracks are pre-recorded on the tracks T1, T2 and T3 of the optical card 107. As such track numbers, there is a type in which the track numbers are recorded only on one side of the respective tracks, but it is convenient when information is recorded or reproduced in a bilateral direction relative to the tracks to record the track numbers on both sides of the tracks as shown in FIG. 2A. It is popular that each track number is error-correction-encoded to enhance the reliability of the identification and the same number is recorded a plurality of times. Such track numbers are reproduced and recognized at the start of the scanning of the light spots, i.e., at the beginning of a constant velocity region, and whether the track is a desired track is confirmed. Accordingly, the space between the track numbers on both sides provides an information recording region, and in this region, the light spots are scanned and the recording or reproduction of information is effected.
A description will now be provided of the process until the optical information recording/reproducing apparatus according to the prior art records information on the target track of an optical card. When a recording command is first issued from a host control apparatus (for example, a host computer) and recording data is transferred, the process of adding an error correction code to the recording data is carried out by an error encoder in the apparatus. As the error correction code, use is made, for example, of a Reed-Solomon product code, a difference set cyclic code or the like. When the process of adding the error correction code is completed, the seek operation for moving an optical head to the target track is effected. When at this time, the target track is T2 in FIG. 2A, the disposition of reproducing spots 110, 112 and 114 is as shown in FIG. 2A. When the optical head arrives at the target track, the seek operation is terminated and the optical head and the optical card are moved along the track direction to each other, and the light spots are scanned over the information tracks T1, T2 and T3.
Assuming here that the light spots have been scanned in the direction of arrow R in FIG. 2A, when acceleration is effected in an acceleration/deceleration region at the right side of FIG. 2A and a predetermined velocity is reached, scanning is effected at a constant velocity, and when a constant velocity region is entered, track numbers Tn1L, Tn2L and Tn3L recorded at the left head of the track are first reproduced at a time. Then, error correction decoding is effected by an error decoder because an error correction code is added to each track number. When the error correction decoding has been completed and it is confirmed from the track numbers that the tracks are T1, T2 and T3, the recording of information is effected on an information recording region.
A description will now be provided of the process until information already recorded on the information recording region of the target track of the optical card is reproduced. When a reproducing command is first issued from the host control apparatus, the seek operation for moving the optical head to the target tracks, as in the case of recording, is effected. If at this time, the target tracks are T1, T2 and T3 in FIG. 2A, the disposition of the reproducing spots 110, 112 and 114 becomes as shown in FIG. 2A. When the optical head arrives at the target tracks, the seek operation is completed and the optical head and the optical card are reciprocally moved in the track direction relative to each other, and the light spots are scanned over the information tracks T1, T2 and T3.
Assuming here that the light spots have been scanned in the direction of arrow R in FIG. 2A, acceleration is effected in the acceleration/deceleration region at the left side of FIG. 2A, as in the case of recording, and when a predetermined velocity is reached, scanning is effected at a constant velocity. When the constant velocity region is entered, track numbers Tn1L, Tn2L and Tn3L recorded at the left heads of the tracks are first reproduced, whereafter error correction decoding is effected by the error decoder because an error correction code is added to each track number. When the error correction decoding is completed and it is confirmed from the track numbers that the tracks are T1, T2 and T3, the reproduction of information already recorded on the information recording regions of the tracks T1, T2 and T3 is effected.
Now, in the prior art, when recording or reproduction is to be effected on an optical card, the respective track numbers of three tracks are reproduced at the beginning of the constant velocity region and the error correction decoding of all the three reproduced track numbers is effected to thereby determine whether the track is a desired track. Such determination of the track must be completed within a period during which the light spot passes through the gap portion between the track number portion and the data portion. However, if an attempt is made to make the relative movement velocity of the optical head and the optical card higher to improve throughput, the time during which the light spot passes through the gap portion will become short. Therefore, the time will become deficient to effect the deterioration of all of three tracks, and this has led to the problem that the light spot arrives at the data portion before the determination of the tracks is completed, and the recording or reproduction of information becomes impossible. Also, to shorten the time for determining the tracks, a CPU (central processing unit) and an error correction decoder can be made higher in speed, but such a method has led to the problem of higher cost.